1. Field
The present disclosure relates to a flat panel display, specifically, to a display driven by varying voltage levels.
2. Description of the Related Technology
Organic light emitting display devices display images using organic light emitting diodes (OLEDs) that emit light through recombination of electrons and holes. Since the OLED display device has a fast response speed and is driven with low power consumption, if it has been identified as a next-generation display.
Generally, the OLED display device includes a pixel unit having a matrix of pixels, driving circuits for supplying driving signals to the pixel unit, and a power supply circuit for supplying pixel power to the pixel unit.
When a scan signal is supplied to each pixel, the pixel is synchronized with a gate signal so as to emit light with luminance corresponding to a data signal.
However, in the OLED display device, the emission luminance of the pixels is influenced by the applied voltage level. That is, the voltage applied to a pixel, or pixel power, becomes a factor in the resulting emission luminance of the pixels, in addition to the data signal.
Therefore, the same voltage should be applied to each pixel so as to display images having uniform image quality.
However, pixel power is a DC voltage determined by the difference between a power supply voltage having a high voltage level and a ground voltage having a low voltage level. While passing through a power line, a voltage drop (IR drop) occurs in the power voltage, and a voltage rise (IR rise) occurs in the ground voltage.
In the case where the voltage drop and the voltage rise overlap with each other, the luminance inequality of the display panel increases, and white spots may be locally produced.
Particularly, as the display panel of the display device becomes large in size, the length of the power line is lengthened, and therefore, the difference in luminance between the pixels may be increased according to distances from power pads for receiving pixel power supplied from the power supply circuit.